Interference suppression methods for 802.11

ABSTRACT

An 802.11 source station transmits a message, such as a CF-End message, to reset a network allocation vector at a time other than that required for indicating the end of the contention free period. That is, the source station uses the CF-End message to spoof stations within range of the message into resetting the stations&#39; network allocation vectors as if the contention free period were active. Thus, the spoofing source station is allowed to release the medium for general use after the medium has been reserved for a specific use, for a greater time than necessary. Accordingly, spoofed stations may, for example, 1) delay transmission until a more critical transmission has completed, 2) allow unknown or foreign protocol to have preferential use of the medium, 3) prevent interference from hidden stations, and 4) allow sharing of the medium by overlapping basic service sets. After the specific use, if the medium is still reserved, the medium may be released for general use.

This application claims the benefit of U.S. Provisional Application No.60/261936, filed Jan. 16, 2001, entitled Interference SuppressionMethods For 802.11, U.S. Provisional Application No. 60/261901, filedJan. 16, 2001, entitled Interference Suppression Methods For 802.11, andU.S. Provisional Application No. 60/262604, filed Jan. 18, 2001,entitled Interference Suppression Methods For 802.11, which areincorporated by reference herein in their entirety. This application isrelated to U.S. application entitled Interference Suppression MethodsFor 802.11, which is filed on even date herewith. These two applicationsare co-pending and commonly assigned.

BACKGROUND OF THE INVENTION

Wireless local area networks (WLANs) employ a plurality of mobilenetwork stations, such as data processing devices having wirelesscommunication capabilities. Access to the wireless medium in such anetwork is controlled in each station by a set media access control(MAC) protocol based on a listen-before-talk scheme.

IEEE 802.11 is a well-established standard for implementing media accesscontrol. An enhanced version of the 802.11 standard is the 802.11estandard.

SUMMARY OF THE INVENTION

In development of quality of service enhancements for the existing802.11 standard, it is desirable to guarantee the time a packet or framewill be delivered on the wireless local area networks. However, when newprotocols within new versions such as the enhanced 802.11e standard areintroduced, there may be stations on the wireless local area networksthat may not understand these new protocols. That is, there may be olderstations in the wireless local area network that may not be equipped topractice the enhanced 802.11e standard. Furthermore, not all newstations practice the enhanced 802.11e standard. Accordingly, the olderstations or stations not practicing the enhanced 802.11e standard mightinterfere with the enhanced 802.11e protocols.

Thus, interference may occur that may prevent reception of anotherdesired transmission, or that may cause another transmission to bedelayed, so that the delayed transmission is no longer useful oncereceived.

In accordance with the various exemplary embodiments of this invention,while a first source station is transmitting on a medium, transmissionfrom a second source station that is not equipped to practice theenhanced 802.11e standard, or that does not practice the enhanced802.11e standard, is prevented from starting while the first sourcestation is still using the medium. Thus, in accordance with the variousexemplary embodiments of this invention, loss of a packet from beingreceived by a destination station due to the interference from a secondsource station is prevented.

In accordance with the exemplary embodiments of this invention, virtualcarrier detection to determine a medium's availability for transmissionis implemented using the 802.11 frames. In these exemplary embodiments,using clear channel assessment, the source station desiring to use themedium will not transmit until it determines that the medium is clear,i.e., when it determines that no carrier or significant signal ispresent. In accordance with the exemplary embodiments of this invention,transmissions earlier in a sequence are provided with informationconcerning the transmissions later in the sequence, whereby informationconcerning the later transmissions is used to determine the medium'savailability.

In various exemplary embodiments of this invention, an 802.11 durationfield may be used to indicate periods of time when no carrier may bepresent, or a non-802.11 carrier may be present on the medium. Forexample, a source station may use the duration field to indicate timeswhere if a transmission is begun from the source station, the sourcestation may cause delay in another transmission.

In accordance with these various exemplary embodiments of thisinvention, an 802.11 source station transmits a signal with a durationfield other than that required for the transmission to preventtransmission by other stations during known sequences. In accordancewith these exemplary embodiments, a duration field is used to “spoof”,or misrepresent the actual time the medium will be occupied, to stationswithin range of the signal.

In accordance with other exemplary embodiments, a specific set of 802.11stations, rather than all stations within range of the signal, areinvolved in the spoofing scheme. In accordance with other variousexemplary embodiments of this invention, the application of the durationfield may be further generalized to apply to specific sets of stations.By applying group addressing with a duration field, sets of stations aredetermined as to whether the stations should obey the duration field setin the signal. Thus, a specific group of stations could be caused tosuppress transmission.

In accordance with other exemplary embodiments of this invention, an802.11 CF-End message may be used to indicate the end of the period oftime for suppressing transmission. For example, a source station may usethe CF-End message to indicate times where if a transmission from thesource station has ended as well as after the delay of othertransmissions, the source station may cause transmissions from allstations that had suppressed their transmissions to resume transmittingby resetting a suppression mechanism.

In accordance with these various exemplary embodiments of thisinvention, an 802.11 source station transmits a CF-End message toindicate the end of the period of time for suppressing transmission fromother stations other than that representing the end of thecontention-free period. That is, in accordance with these exemplaryembodiments, the CF-End message is used to misrepresent to stationswithin range of the signal the actual reset time for resetting thenetwork allocation vectors (NAV).

In accordance with other various exemplary embodiments, group addressingis provided that only stations in a particular group are caused to resettheir suppression mechanism.

In accordance with the various exemplary embodiments of this invention,a station within range of the transmitted signal will check the durationfield and the CF-End message of the transmitted signal, and update thestation's network allocation vector (NAV). Thus, a spoofed station willnot transmit because the station's network allocation vector indicatesthat the medium is in use, even though the station maybe unable to hearthe carrier.

In accordance with the various exemplary embodiments of this invention,because their network allocation vectors indicate that the medium is inuse, stations within range of the spoofed signal, including hiddenstations, will be spoofed into suppression, thereby not interfering withunknown or foreign protocols. That is, in accordance with theseembodiments, spoofed stations may, for example, 1) delay transmissionuntil a more critical transmission has completed, 2) allow unknown orforeign protocol to have preferential use of the medium, 3) preventinterference from hidden stations, and 4) allow sharing of the medium byoverlapping basic service sets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a wireless local area network.

FIG. 2 shows an exemplary embodiment of a station in the wireless localarea network.

FIG. 3 shows detailed operation of the method to exchange controlinformation when transmitting data from a transmitting station to areceiving station.

FIG. 4 shows an exemplary embodiment of the request-to-send (RTS) frameformat.

FIG. 5 shows an exemplary embodiment of the clear-to-send (CTS) frameformat.

FIG. 6 shows one exemplary method of enhancing the signal transmissionaccording to this invention.

FIG. 7 shows another exemplary method of enhancing the signaltransmission according to this invention.

FIG. 8 shows a flow chart of an exemplary method of enhancing the signaltransmission according to this invention.

FIG. 9 shows a flow chart of another exemplary method of enhancing thesignal transmission according to this invention.

FIG. 10 shows a flow chart of another exemplary method of enhancing thesignal transmission according to this invention.

DETAILED DESCRIPTION

FIG. 1 discloses an exemplary embodiment of a wireless local areanetwork (WLAN). It should be appreciated that various types of localarea networks for forwarding messages to and receiving messages fromnetwork stations may be employed in the various exemplary embodiments ofthis invention.

As shown in FIG. 1, the wireless local area network 10 includes adistribution system 100, stations 160-1 and 160-2 provided in a firstbasic service set BSS1 having the same basic service, and stations 160-3and 160-4 provided in a second basic service set BSS2 having the samebasic service. For example, stations 160-1 and 160-2 are networkstations provided within a cell under a common coordinating function,with one of the stations providing access to the distribution system 100being an access point (AP) to a basic service set. Similarly, stations160-3 and 160-4 are network stations provided within a cell under acommon coordinating function, with one of the stations providing accessto the distribution system 100 being an access point (AP) to a secondbasic service set. Stations 160-1 to 160-4 together with thedistribution system 100 form an extended service set (ESS), where allstations may communicate with each other without involving entitiesoutside of the 802.11 media access control (MAC) architecture. It shouldbe appreciated that any of the stations 160-1 to 160-4 that are notaccess points may also be mobile network stations.

Further, it should be appreciated that the stations 160-1, 160-2, 160-3and 160-4 may be connected to other devices and/or networks with whichthe stations may communicate. Furthermore, though FIG. 1 only shows fourstations within the wireless local area network 10, it should beappreciated that a wireless local area network may include more thanfour stations. That is, it should be appreciated that the basic servicesets BSS1 and BSS2 may each include more than two stations in accordancewith this invention.

As shown in FIG. 1, stations 160-2 and 160-3 are also access points (AP)that provide access to the distribution system 100 by the basic servicesets BSS1 and BSS2, respectively. The distribution system 100 enablesmobile network station support to the mobile network stations 160-1 and160-4 by providing the logical services necessary to handle address todestination mapping and seamless integration of multiple basic servicesets. Data moves between the basic service sets BSS1 and BSS2 and thedistribution system 100 via access points. In accordance with theseexemplary embodiments, because the access points are also stations 160-2and 160-3, they are addressable entities. It should be appreciated thatthough FIG. 1 shows basic service sets BSS1 and BSS2 as two separatesets, in accordance with various exemplary embodiment of this invention,the basic service sets may partially overlap, be physically disjointed,or be physically collocated.

As shown in FIG. 1, to send a data message from station 160-1 to station160-4, for example, the message is sent from station 160-1 to station160-2, which is the input access point for basic service set BSS1 to thedistribution system 100. Station 160-2, as an access point, gives themessage to the distribution service of the distribution system 100. Thedistribution service delivers the message within the distribution system100 in such a way that the message arrives at the appropriatedistribution system destination for the intended station, station 160-4.In the exemplary embodiment of FIG. 1, the message is distributed by thedistribution service to station 160-3, which is the output access pointfor basic service set BSS2, and station 160-3 accesses a wireless mediumto send the message to the intended destination, station 160-4.

FIG. 2 discloses an exemplary embodiment of a station in the wirelesslocal area network, such as a mobile network station. As shown in FIG.2, a station 200 is provided with an antenna 220, a receiving unit 240,a transmitting unit 260, and a central processing unit (CPU) 280. Themobile network station 200 selectively transmits and receives messages.

When receiving data, a signal received by the mobile network station 200is received by the antenna 220, demodulated into control information ordata through the receiving unit 240. Based on the control informationaddressed at the receiving unit 240, the central processing unit (CPU)280 controls receipt of data by the receiving unit 240.

In transmitting data, the central processing unit (CPU) 280 identifieswhether or not the medium is unused for a time period. If the centralprocessing unit (CPU) 280 determines that the medium is busy, thecentral process unit (CPU) 280 proceeds to defer mode, while if thecentral processing unit (CPU) 280 detects that the medium is unused foran appropriate period of time, the transmitting unit 260 transmits data.

FIG. 3 shows detailed operation of the method to exchange controlinformation when transmitting data from a transmitting station to areceiving station, according to an exemplary embodiment of thisinvention. As shown in FIG. 3, a request-to-send signal (RTS) 81 is usedby a transmitting station as control information for identifying themedium connectability to a receiving station. A clear-to-send signal(CTS) 82 is used by the receiving station as control information forresponding to the identification made by the request-to-send signal(RTS) 81. Data 83 is sent by the transmitting station after theclear-to-send signal (CTS) 82 has been sent. An acknowledgment signal(Ack) 84 is used by the receiving station as control information foracknowledging the data reception of data 83. Subsequent data issubjected to a succeeding procedure started by another station afterconfirming termination of the transmission procedure between thetransmitting and receiving stations, as acknowledged by theacknowledgment signal (Ack) 84 from the receiving station.

As shown in FIG. 3, time intervals such as inter-frame spaces (IFS) areprovided between frames. A station determines that the medium is idlethrough the use of the virtual carrier detection to determine a medium'savailability for transmission for the interval specified. As shown inFIG. 3, the inter-frame spaces (IFS) may include short inter-framespaces (SIFS), PCF inter-frame spaces (PIFS), and DCF inter-frame spaces(DIFS).

As shown in FIG. 3, short inter-frame spaces (SIFS) are used as gapsbetween exchange procedures. For example, as shown in FIG. 3, the shortinter-frame spaces (SIFS) 816, 812, and 813 are used respectively asgaps between the request-to-send (RTS) frame 81, the clear-to-send (CTS)frame 82, the data frame 83, and the acknowledgment (Ack) frame 84, forexample. A short inter-frame space (SIFS) indicates the time from theend of the last symbol of the previous frame to the beginning of thefirst symbol of the preamble of the subsequent frame as seen at the airinterface. The short inter-frame space (SIFS) is the shortest of theinter-frame spaces and is used when stations have seized the medium andneed to keep the medium for the duration of the frame exchange sequenceto be performed. Using the smallest gap between transmissions within theframe exchange sequence prevents other stations, which are required towait for the medium to be idle for a longer gap, from attempting to usethe medium, thus giving priority to completion of the frame exchangesequence in progress.

As shown in FIG. 3, DCF inter-frame spaces (DIFS) are used by stationsoperation under the distributed coordination function (DCF) to transmitdata frames and management frames. A station using the distributedcoordination function (DCF) transmits a data frame if the virtualcarrier detection mechanism determines that the medium is idle. As shownin FIG. 3, at a starting point of the exchange procedure from atransmitting station to a receiving station, DCF inter-frame space(DIFS) 811 is spent for confirming connectability (channel occupationstatus) on the medium for transmission of the request-to-send signal(RTS) 81. Further, as shown in FIG. 3, after data 83 has been delivered,supplemental DCF inter-frame space (DIFS) 814 is spent, and the stationperforms a backoff procedure.

A data frame format comprises a set of fields that occur in a fixedorder in all frames. These fields are used to indicate theidentification of the basic service set, the address of the sourcestation, the address of the destination station, the address of thetransmitting station and the address of the receiving station, forexample. FIGS. 4 and 5 show exemplary embodiments of the frame formatsaccording to this invention.

FIG. 4 shows an exemplary embodiment of the request-to-send (RTS) frameformat. As shown in FIG. 4, the request-to-send (RTS) frame 400 includesa frame control field 410 for frame control, a duration field 420 forthe duration, a receiving station address field 430 for the address ofthe receiving station, a transmitting station address field 440 for theaddress of the transmitting station, and a frame check sequence field450 as a calculation field for a parity check. In the request-to-sendframe format of FIG. 4, the receiving station address is the address ofthe station that is the intended immediate recipient of the pendingdirected data or management frame. The transmitting station address isthe address of the station transmitting the request-to-send (RTS) frame400.

FIG. 5 shows an exemplary embodiment of the clear-to-send (CTS) frameformat. As shown in FIG. 5, the clear-to-send (CTS) frame 500 includes aframe control field 510, a duration field 520, a receiving stationaddress field 530, and a frame check sequence field 550. In theclear-to-send (CTS) frame format of FIG. 5, the receiving stationaddress is the address copied from the transmitting station field 440 ofthe immediately previous request-to-send (RTS) frame 400 to which theclear-to-send (CTS) frame 500 is a response.

For a station to transmit, using virtual and physical carrier detection,the station determines if another station is transmitting. If no stationis determined to be transmitting, the transmission may proceed. Thetransmitting station ensures that no other station is transmitting for arequired duration before attempting to transmit. If another station isdetermined to be transmitting, the detecting station defers transmissionuntil the end of the current transmission.

The request-to-send (RTS) and the clear-to-send (CTS) frames 400 and 500are exchanged prior to the actual data frame to distribute mediumreservation information to announce the impending use of the medium. Inaccordance with an exemplary embodiment, the request-to-send (RTS) andthe clear-to-send (CTS) frames 400 and 500 contain a duration field thatdefines the period of time that the medium is to be reserved to transmitthe actual data frame and the returning acknowledgment frame. Allstations within the reception range of either the originating stationwhich transmits the request-to-send (RTS) signal or the destinationstation which transmits the clear-to-send (CTS) frame learns of themedium reservation. Thus, a station can be unable to receive from theoriginating station yet still know about the impending use of the mediumto transmit a data frame.

The request-to-send (RTS) and clear-to-send (CTS) signals 81 and 82contain information to set the network allocation vectors (NAV) for thestations within the range of the signals. In FIG. 3, each networkallocation vector (NAV) field 821 in 822 shows the information containedin the request-to-send (RTS) and clear-to-send (CTS) signals 81 and 82,respectively.

The network allocation vector (NAV) maintains a prediction of futuretraffic on the medium based on duration information that is announced inthe request-to-send (RTS) and clear-to-send (CTS) frames 81 and 82 priorto the actual exchange of data.

A station receiving a valid frame updates the station's networkallocation vector (NAV) with the information received in the durationfield contained in frame. As shown in FIG. 3, stations receiving therequest-to-send (RTS) frame 81 set the network allocation vector (NAV)821 in accordance with the request-to-send (RTS) frame 81, whilestations only receiving the clear-to-send (CTS) frame 82 set theirnetwork allocation vector (NAV) 822 in accordance with the clear-to-send(CTS) frame 82, resulting in the lower network allocation vector (NAV)as show in FIG. 3.

At the nominal beginning of each contention free period (CFP), theaccess point (AP) senses the medium. When the medium is determined to beidle for a period of time, the access point (AP) transmits a beaconframe. After the initial beacon frame, the access point (AP) waits forat least another period of time, and then transmits one of 1) a dataframe, 2) a CF-Poll frame with which the access point (AP) requests oneof the stations to transfer a data packet, 3) 4) a Data+CF-Poll framewhich contains a poll and data for the polled station, or a CF-End framewhich indicates the end of the contention free period (CFP).

In the exemplary embodiment in FIG. 3, at a starting point of theexchange procedure from a transmitting station to a receiving station,DCF inter-frame spaces (DIFS) 811 and 814 are spent in the contentionperiod (CP) for confirming connectability (channel occupation status) onthe medium for transmission of the request-to-send signal (RTS) 81. Inaccordance with other various exemplary embodiments of this invention,to confirm connectability on the medium for transmission of therequest-to-send signal (RTS) 81, shorter PCF inter-frame spaces (PIFS)may be used instead of the DCF inter-frame spaces (DIFS) 811 and 814with the request-to-send signal (RTS) transmission. Thus, by using thePCF inter-frame spaces (PIFS), priority access to the medium may beobtained.

Though the shorter PCF inter-frame spaces (PIFS) are not normally usedoutside of the 802.11 contention free period (CFP) and a request-to-sendsignal (RTS) is normally only transmitted in the contention period (CP),in these exemplary embodiments, a request-to-send signal (RTS) could beused in the contention free period (CFP) or a PCF inter-frame spaces(PIFS) could be used in the contention period (CP) so as to preventvarious stations from transmitting at inappropriate times. In theseembodiments, receiving stations would behave in a predictable manner andwould be suppressed, potentially reducing the possibility ofinterference.

Transmission of a frame from station 160-1 to station 160-2 of FIG. 1,for example, may not be heard by another station wishing to use themedium to transmit subsequent data because the another station may betoo far away, or there may be intervening obstacles. In addition,transmission of the subsequent data may interfere with the transmissionof data 83 if the another station transmitting the subsequent data doesnot understand the protocol of station 160-1 transmitting data 83.Without enhancements, the another station may start to transmit thesubsequent data while the first station, station 160-1, is still usingthe medium. Accordingly, the receiving station for data 83, station160-2, for example, may hear both transmitting stations 160-1 and theanother station transmitting the subsequent data, and the data 83 beingreceived will be lost due to the transmission of the subsequent datafrom the second transmitting station.

As discussed above, in accordance with exemplary embodiments of thisinvention, the request-to-send (RTS) and clear-to-send (CTS) signals 81and 82 include information which indicates the availability of themedium for the subsequent transmission of the subsequent data. Forexample, request-to-send (RTS) and clear-to-send (CTS) signals 81 and 82may include a duration value in the duration field to indicate mediumavailability. A station within the range of the signal will check theduration field of the signal, and update the station's networkallocation vector (NAV) to indicate when the medium is known in advanceto be busy. Then, even if no carrier is sensed on the medium, thestation will not transmit as it knows the medium is in use, even thoughit maybe unable to hear the carrier. That is, in these exemplaryembodiments of this invention, the 802.11 duration field is used toindicate periods of time when no carrier may be present, or a non-802.11carrier may be present, and the duration field is used to suppresstransmissions from stations so as to avoid interference from thesuppressed stations.

FIG. 6 shows one exemplary method of enhancing the signal transmissionaccording to this invention. In this embodiment, the duration field setto a predetermined value other than the duration time for the subsequenttransmissions is sent by a transmitting station, and the stations withinthe range of the sent signal will update their network allocation vector(NAV) in accordance with the set duration field value.

As shown in FIG. 6, the network allocation vector (NAV) for the stationswithin the range of the transmitted signal 80, such as a clear-to-sendsignal (CTS) or request-to-send signal (RTS), is set to be greater thanthe time required for subsequent transmissions Tx1, Tx2, . . . TxN bythe stations within the range. Because the stations within the range andobeying the duration field may believe the duration field represents thetime it will take for transmissions immediately following the sequence,the obeying stations are in essence being spoofed by the transmittingstation. That is, the duration field is not being used by thetransmitting station for its intended purpose of representing the timeit will take for transmissions immediately following the sequence.Rather, the duration field is used by the transmitting station toindicate times to suppress the transmissions Tx1, Tx2, . . . TxN by thestations within the range of the signal 80, where if the suppressedtransmissions Tx1, Tx2, . . . TxN have begun, another more criticaltransmission may be delayed, a protocol other than 802.11 which might beundetectable to the 802.11 station may interfere with the 802.11station, or the transmitting 802.11 stations may interfere with aforeign protocol or advanced 802.11 protocol. Thus, in FIG. 6, duringthe suppressed time period set by the network allocation vector (NAV),transmissions, Tx1, Tx2 . . . TxN from the stations obeying the durationfield are suppressed. By spoofing to the stations obeying the durationfield, it is possible to get the obeying stations to exhibit behaviorfor which it was not originally programmed, such as delaying thetransmissions Tx1, Tx2, . . . TxN until a more critical transmission hascompleted or suppressing transmission so that undetectable protocols maynot interfere.

In the network of FIG. 1, if station 160-2 wishes to prevent anotherstation from causing a beacon from being transmitted beyond the targetbeacon transmit time (TBTT), for example, station 160-2 may send asignal to another station such as station 160-1 containing a durationtime that exceeds the normal requirements of the protocol so as to coverany time remaining between the current time, and the next target beacontransmit time. Station 160-1 and other stations within range of the sentsignal will not realize that the duration field is incorrectly set, andmight even propagate the signal further by re-transmitting the durationfield. Thus, in this example, station 160-2 would send a signal, such asa request-to-send signal (RTS), to station 160-1 with the duration fieldset to cover the remaining time to the target beacon transmit time, andthe receiving station 160-1 would respond with a clear-to-send signal(CTS) whose duration would be set to cover the remaining time to thetarget beacon transmit time as well. All stations within range of therequest-to-send signal (RTS), clear-to-send signal (CTS), or both wouldset their network allocation vectors (NAV) so as not to attempttransmission again until after the target beacon transmit time.

In accordance with other exemplary embodiments of this invention, theapplication of the duration field may be further generalized to apply tospecific sets of stations rather than all stations within range. Thatis, in accordance with these exemplary embodiment, only specific sets ofstations are spoofed by the duration field. For example, enhancedstations under the 802.11e or later standard could apply groupaddressing with the duration field to determine which sets of stationsshould obey the duration field, and which should ignore it. Thus, aspecific group of stations, such as legacy stations which do not applythe enhanced 802.11e standard, could be caused to suppress transmission.That is, because stations applying the enhanced 802.11e standards mayalready contain protocols that prevent them from transmitting at asuppressed time and the legacy stations which do not apply the enhanced802.11e standards do not contain these protocols, these legacy stationsmay be treated as a special group. In this case, the transmittingstation sends the signal only to the group of legacy stations.

A transmitting station wishing to block usage of the medium by a set ofstations sets the duration field for the length of time during whichusage of the medium is to be restricted. Other parameters in thetransmission determine which specific group of stations should recognizethe value of the duration field. Stations not in this specific groupwould ignore the value of the duration field. Thus, in the example ofFIG. 6, if the transmitting station wishes to block usage of the mediumby a group of legacy stations, suppressed transmissions Tx1, Tx2 . . .TxN within the time period set by the network allocation vector (NAV)would only be transmissions from legacy stations.

In an exemplary embodiment, a transmitting station such as an accessport (AP) may send a signal, such as the clear-to-send signal (CTS), toa group address. In group addressing, the station transmitting to thegroup address has access to lists of assigned group addresses and theproperties for membership in each of these addresses. A station withinrange of the clear-to-send (CTS) signal may identify if the receivingstation address (RA) of the sent signal is a group address and whetheror not the station belongs to that group. A specific set of stations,such as the stations applying an enhanced 802.11e standard, would ignorethe duration field of the clear-to-send signal (CTS) if the receivingstation address (RA) in a clear-to-send signal (CTS) were set to thegroup address. The specific set of stations would then surmise that thetransmitting station was spoofing the stations that are not applying theenhanced 802.11 standards, such as legacy stations. The stationsapplying the enhanced 802.11 standards would ignore the duration fieldin the clear-to-send signal clear-to-send (CTS), and still would be freeto transmit. Since stations applying the enhanced 802.11 standards inaccordance with this invention know not to delay the beacon from thetransmitting access port (AP), the stations applying the enhanced 802.11standards are free to use the medium. On the other hand, legacy stationsand other stations which do not apply the enhanced 802.11 standardswould not detect that they are being spoofed, and would set theirnetwork allocation vectors for the duration value in the clear-to-sendsignal (CTS) so as not to transmit. Thus, the spoofed stations areprevented from transmitting at the target beacon transmit time anddelaying the beacon from the transmitting access point (AP).

Table 1 shows an exemplary embodiment of the effects of a clear-to-send(CTS) signal on stations within range of the signal. It should beappreciated that since a legacy station (LSTA) will always set itsnetwork allocation vector (NAV) according to the received signal,effects on legacy stations are not shown in Table 1.

TABLE 1 Message RA Effect CTS STA Set NAV CTS group Set NAV if not inGroup CTS broadcast Set if legacy station

As shown in Table 1, when a clear-to-send (CTS) signal is transmitted,if a station (STA) identifies that the receiving station address (RA) inthe clear-to-send (CTS) signal is the station's own address, that is, aunicast address, the station will set the station's network allocationvector (NAV) in accordance with the received clear-to-send (CTS) signal.If the station identifies that the receiving station address (RA) of theclear-to-send (CTS) signal is that of a group address, that is, amulticast address, the station will set the network allocation vector(NAV) if the station is not in the addressed group. Alternatively, theprotocol may be defined such the station sets its network allocationvector (NAV) if the station is a member of the multicast address. If thereceiving station address (RA) of the clear-to-send (CTS) signal is abroadcast address, the station will set it network allocation vector(NAV) only if it is a legacy station that does not practice the enhanced802.11e standard.

It should be appreciated that, while a station transmitting aclear-to-send signal (CTS) may usually expect signals sent in response,in accordance with the various exemplary embodiments of this invention,the clear-to-send signal (CTS) is merely sent for setting the networkallocation vector (NAV), and thus, no other responses are expected bythe station transmitting a clear-to-send signal (CTS). It should beappreciated that similar provisions with, for example, 802.11 data ornull frame, that is a data frame containing no data, may be applied inaccordance to this invention.

In accordance with other exemplary embodiments of this invention, arequirement for resetting network allocation vectors when aclear-to-send (CTS) signal is not detected after a request-to-send (RTS)signal, or when no frame is detected within a predetermined time periodof a request-to send (RTS) signal, is added. In an example, if some ofthe stations in a basic service set (BSS) are legacy stations whichrequire resetting the network allocation vectors when a clear-to-send(CTS) signal is not detected, an additional message may be sent to thebroadcast address. This additional clear-to-send (CTS) signal or anyother similarly encoded frame may be transmitted immediately after theclear-to-send (CTS) signal response to the request-to-send (RTS) signal,or otherwise may immediately follow the request-to-send (RTS) signal. Astation not hindered by this requirement, such as stations practicingenhanced 802.11e standards, may not be affected by the additionalclear-to-send signal (CTS), since the additional clear-to-send (CTS)signal contains a duration value corresponding to the same network timefor resetting of the network allocation vector (NAV) as the priorrequest-to-send (RTS) and clear-to-send (CTS) signals. The stationsreceiving the clear-to-send (CTS) signal may defer resetting theirnetwork allocation vectors until the desired duration had expired.

It should be appreciated that this invention is not limited to theclear-to-send (CTS) signal, and that other message types such as a null,acknowledgement signal or data frames could be used to perform the samefunction as the clear-to-send (CTS) signal.

Table 2 shows an exemplary embodiment of the effects of arequest-to-send (RTS) signal on stations within range of the signal. Itshould be appreciated that other similar encodings may be developed bythose skilled in the art using the principles disclosed in thisinvention. As in Table 1, since a legacy station will always set itsnetwork allocation vector (NAV) according to the received signal,effects on legacy station are not shown in Table 2.

TABLE 2 Message TA RA Effect RTS unicast1 unicast1 Set NAV if not insame BSS RTS unicast1 unicast2 Set NAV, Respond CTS, obey NAV for CTSRTS unicast1 multicast1 Set NAV if not in Group RTS unicast1 broadcastSet NAV RTS multicast1 unicast1 Set NAV if not in Group, send CTS toGroup, ignore NAV for CTS, obey physical CCA RTS multicast1 multicast1Set NAV if not in Group, send CTS to Group, ignore NAV for CTS, obeyphysical CCA RTS multicast1 multicast2 Set NAV if not in Group, send CTSto Group, ignore NAV for CTS, obey physical CCA RTS multicast1 broadcastSet NAV RTS broadcast unicast1 Set NAV if not in same BSS RTS broadcastmulticast1 Set NAV if not in same Group RTS broadcast broadcast Set NAV

As shown in Table 2, when a request-to-send (RTS) signal is transmitted,a station identifies the transmitting station address (TA) and thereceiving station address (RA) in the request-to-send (RTS) signal, andsets the station's network allocation vector (NAV) accordingly. As shownin Table 2, if the transmitting station address (TA) is of a firstunicast address (unicast1), the station will set its network allocationvector (NAV) if 1) the receiving station address (RA) is a broadcastaddress, 2) the receiving station address (RA) is also of the firstunicast address (unicast1) and the station is in the same basic serviceset as the first unicast address (unicast1), or 3) if the receivingstation address (RA) is a multicast address (multicast1) and the stationis not in the same group as the addressed group. Further, if thereceiving station address is another unicast address (unicast2), thestation will set its network allocation vector (NAV) accordingly,respond with a clear-to-send (CTS) signal if the station's address isthe another unicast address (unicast2), and obey the network allocationvector (NAV) in the clear-to-send (CTS) signal.

As shown in Table 2, if the transmitting station address (TA) is of afirst multicast address (multicast1), the station will set its networkallocation vector (NAV) if the receiving station address (RA) is abroadcast address. Further, if the receiving station address (RA) isalso of the first multicast address (multicast1) or another multicastaddress (multicast2), or a unicast address (unicast1), the station willset its network allocation vector (NAV) accordingly if the station isnot in the addressed group of the first multicast address (multicast1),respond with a clear-to-send (CTS) signal if addressed by the receivingstation address (RA), ignore the network allocation vector (NAV) fortransmitting the clear-to-send (CTS) signal, but obey physical clearchannel assessment (CCA). It should be appreciated that it is alsopossible to encode the message such that the network allocation vector(NAV) is set if the station is in the addressed group of the firstmulticast address (multicast1).

Further, as shown in Table 2, if the transmitting station address (TA)is of a broadcast address (Broadcast), the station will set its networkallocation vector (NAV) if 1) the receiving station address (RA) is abroadcast address, 2) the receiving station address (RA) is also of thefirst unicast address (unicast1) and the station is in the same basicservice set as the first unicast address (unicast1), or 3) if thereceiving station address (RA) is a multicast address (multicast1) andthe station is not in the same group as the addressed group.

It should be appreciated that the use of the techniques of thisinvention could be for sharing with a non-802.11 protocol. If the mediumis to be reserved for a period of time for use by a non-802.11 protocol,the transmitting station could send a message with the duration fieldset so as to prevent use of the medium by 802.11 stations when anotherprotocol is active. For example, as shown in FIG. 7, a stationpracticing the enhanced 802.11e standards could send a signal 80, suchas a clear-to-send signal (CTS), to itself with a duration field set toa specified duration value. All stations including stations practicingthe enhanced 802.11e standards would set their network allocationvectors (NAV) accordingly. The other unknown or foreign protocol wouldthen have preferential use of the medium during that specified durationvalue interval. The stations practicing the 802.11 standards within therange of the clear-to-send signal (CTS) would set their networkallocation vectors so as not to use the medium, even thought they mightnot be able to detect the other protocol.

It should be appreciated that, in accordance with this invention, astation practicing an 802.11e standard or some future enhanced 802.11version may introduce a new protocol within the standard. For example, atoken passing scheme may be introduced within the 802.11e enhancedstandard, or an unscheduled contention free period (CFP) may beintroduced between a transmitting station, such as the access point(AP), and a subset of stations. In accordance with various exemplaryembodiments of this invention, the new protocol is specific to a groupof stations, and stations that are not in the specific group are set tosuppress transmissions. In these exemplary embodiments, the transmittingstation may send a request-to-send signal (RTS) from itself, forexample, to the group's multicast address in which the duration timewould be set for a specific extended period of time. Stations not in thegroup are set to suppress transmissions, while the transmitting stationimplements a protocol of its choosing.

In other exemplary embodiments of this invention, an 802.11 CF-Endmessage may be used to indicate the end of the period of time forsuppressing transmission other than the time indicated by the durationvalue. That is, though the CF-End message is normally only used in the802.11 standards to indicate the end of the contention free period(CFP), in accordance with these embodiments, the CF-End message may beused for other purposes. For example, a source station may use theCF-End message to indicate times where if a transmission from the sourcestation has ended and no further delay of other transmissions isrequired, the source station may cause transmissions from all stationsthat had suppressed their transmissions to resume transmitting byresetting a suppression mechanism.

In accordance with the various exemplary embodiments of this invention,the 802.11 source station transmits a CF-End message at times other thanthe times indicating expiration of the contention free period (CFP), toprevent transmission by other stations during known sequences. That is,in accordance with these exemplary embodiments, the CF-End message isalso used to spoof stations within range of the signal by lying aboutthe ending of the contention free period (CFP). A station within rangeof the CF-End signal will update the station's network allocation vector(NAV) to indicated the reset time of the network allocation vector(NAV).

Thus, if a transmitting station decides that it no longer needs theadditional time set aside by the duration field in the request-to-sendsignal (RTS), for example, the transmitting station may send a CF-End tothe broadcast address. The CF-End would cause all stations within therange of the CF-End signal to reset the stations' network allocationvectors so as to shorten the time set aside from that originallyspecified in the duration field. Similarly, if the previous transmissionhas ended but the network allocation vector (NAV) has not indicated theend of the suppression duration, as set by the CF-End signal, thestation will not transmit because the station's network allocationvector indicates that the medium is still in use.

It should be appreciated that the application of the enhanced CF-Endalso can be extended to group addressing so that only stations in aparticular group are caused to reset their suppression mechanism.

Table 3 shows an exemplary embodiment of the effects of a CF-End signalon stations within range of the signal. As in Table 1 and Table 2, sincea legacy station will always set its network allocation vector (NAV)according to the received signal, effects on legacy station are notshown in Table 3.

TABLE 3 Message TA RA Effect CF-End unicast1 unicast1 Reset NAV if insame BSS CF-End unicast1 unicast2 Reset NAV if unicast2 CF-End unicast1multicast1 Reset NAV if in Group CF-End unicast1 broadcast Reset NAVCF-End multicast1 unicast1 Reset NAV if in Group CF-End multicast1multicast1 Reset NAV if in Group CF-End multicast1 multicast2 Reset NAVif in Group2 CF-End multicast1 broadcast Reset NAV CF-End broadcastunicast1 Reset NAV if not in same BSS CF-End broadcast multicast1 ResetNAV if not in same Group CF-End broadcast broadcast Reset NAV

As shown in Table 3, when a CF-End signal is transmitted, a stationidentifies the transmitting station address (TA) and the receivingstation address (RA) in the CF-End signal, and sets the station'snetwork allocation vector (NAV) accordingly. As shown in Table 3, if thetransmitting station address (TA) is of a first unicast address(unicast1), the station resets its network allocation vector (NAV) if 1)the receiving station address (RA) is a broadcast address, 2) thereceiving station address (RA) is also of the first unicast address(unicast1) and the station is in the same basic service set as the firstunicast address (unicast1), or 3) if the receiving station address (RA)is a multicast address (multicast1) and the station is in the same groupas the addressed group. Further, if the receiving station address isanother unicast address (unicast2), the station resets its networkallocation vector (NAV) accordingly if the address of the station is thesecond unicast address (unicast2).

As shown in Table 3, if the transmitting station address (TA) is of afirst multicast address (multicast1), the station resets its networkallocation vector (NAV) if 1) the receiving station address (RA) is abroadcast address, 2) the receiving station address (RA) is also of thefirst unicast address (unicast1) and the station is in the same group asthe addressed group, or 3) if the receiving station address (RA) is alsothe first multicast address (multicast1) and the station is in the samegroup as the addressed group. Further, if the receiving station addressis another multicast address (multicast2), the station resets itsnetwork allocation vector (NAV) accordingly if the station is in thesecond group.

As shown in Table 3, if the transmitting station address (TA) is of abroadcast address (Broadcast), the station resets its network allocationvector (NAV) if 1) the receiving station address (RA) is a broadcastaddress, 2) the receiving station address (RA) is also of the firstunicast address (unicast1) and the station is not in the same basicservice set as the first unicast address (unicast1), or 3) if thereceiving station address (RA) is a multicast address (multicast1) andthe station is not in the same group as the addressed group.

It should be appreciated that the methods of this invention may beapplied in overlap mitigation of basic service sets (BSS). That is, themethods may be applied when two or more 802.11 basic service sets (BSS)operate in the same area. In such cases, in accordance to variousexemplary embodiments of this invention, the transmitting stations treateach other as foreign protocols, and suppress transmissions within theirown basic service sets (BSS) at scheduled times as discussed above.Thus, in the example shown in FIG. 6, the suppressed transmissions Tx1,Tx2, . . . TxN are thus transmissions within each basic service set(BSS). In these embodiments, the basic service sets (BSS) may take turnssharing the medium.

In an exemplary embodiment, the station groups are defined as allstations existing in a basic service set that interfere with other basicservice sets. In this exemplary embodiment, group addresses are assignedcorresponding to each of the groups. When a first basic service set anda second basic service set of a plurality of basic service sets arrangea time such that the first basic service set is to suppress interferingtransmissions, the transmitting station for the first basic service setmay issue a signal such as a clear-to-send (CTS) signal to the groupdefined as interfering with the second basic service set. Thus, theimpact to the first basic service set is minimized, as only stationsinterfering with the second basic service set are suppressed.

It should be appreciated that the network allocation vector (NAV) for agiven station may continually be set, due to suppression for theContention Free Period (CFP) from several surrounding basic service sets(BSS). Accordingly, the continually set station may never have thechance to transmit.

In accordance with other various exemplary embodiments of thisinvention, a suppressed station may send a signal, such as aclear-to-send (CTS) signal, in response to a request-to-send (RTS)signal from the access point (AP) of the suppressed station's own basicservice set (BSS), to the stations addressed from one of the groupssuppressing it. That is, the suppressed station would send aclear-to-send signal (CTS) to the group indicated by the transmittingstation, ignoring the suppressed station's own network allocation vector(NAV). The suppressed station would first wait for the medium to bephysically clear of any messages using physical carrier sense on themedium. When the access point (AP) from the suppressed station's ownbasic service set (BSS) hears the clear-to-send (CTS) signal from thesuppressed station, the access point (AP) would then know that one setof interfering stations were suppressed. The access point (AP) thensends a CF-End message from itself, to the suppressed station. Thiswould clear the suppressed station's network allocation vector (NAV),and allow the cleared station to transmit for some period of time. Thetransmitting station may repeat this process with several groups ofinterfering stations in a row if necessary until the cleared stationscould transmit in a clear medium.

In essence, in accordance with the various exemplary embodiments of thepresent invention, the use of signals such as the request-to-send signal(RTS), the clear-to-send signal (CTS), and CF-End would create anunscheduled contention free period (CFP), that could be used toimplement the normal contention free period (CFP) protocol, or anotherprotocol that might be of use in future versions of the 802.11 standard.

It should be appreciated that enhanced stations according to variousexemplary embodiments of this invention may be sensitive to why anetwork allocation vector (NAV) is set. If, for example, the enhancedstation could differentiate between the network allocation vector (NAV)being set because it was in a contention free period (CFP) or being setby a recently transmitted message frame such as data, request-to-sendsignal request-to-send (RTS), or clear-to-send signal (CTS), forexample, it may chose to ignore the network allocation vector (NAV) onlyfor the contention free period (CFP), and obey the network allocationvector (NAV) if it would interrupt an ongoing 802.11 frame exchangesequence. In this example, the standard practice of transmitting theclear-to-send signal (CTS) after a short inter-face time interval (SIFS)would be used. However, if clear channel assessment were not idle, orthe network allocation vector (NAV) was causing suppression due to anongoing frame exchange sequence, no clear-to-send signal (CTS) responsewould occur. Thus, according to these various exemplary embodiments ofthis invention, the station transmitting the request-to-send signal(RTS) would realize that if no clear-to-send signal (CTS) response isheard after a short inter-face time interval (SIFS), the station must besuppressed. At that point, the transmitting station could either retrythe request-to-send signal (RTS) or give up until a later time.

It should be appreciated that in accordance with these exemplaryembodiments, a PCF inter-face time interval (PIFS) may be used for theretry to maintain access priority on the medium, even outside of thecontention free period (CFP), and that the request-to-send (RTS) andclear-to-send (CTS) frames may also be allowed within the contentionfree period (CFP).

FIG. 8 is a flowchart illustrating a method of updating the networkallocation vector (NAV) in accordance with an exemplary embodiment ofthis invention. As shown in FIG. 8, the process begins with step 800,and continues to step 810, where the duration value is set. That is, inthis step, the duration value is set to a value other than a time periodfor subsequent transmission to spoof obeying stations. Control thencontinues to step 820.

In step 820, a signal, such as the clear-to-send (CTS) signal is sentcontaining the set duration value. Next, in step 830, a determination ismade as to whether the receiving station address (RA) in the signal isthat of the station. If the receiving station address (RA) is that ofthe station, control jumps to step 860, where the network allocationvector (NAV) is updated. If not, the receiving station address (RA) isnot that of the station, control continues to step 840.

In step 840, a determination is made as to whether the receiving stationaddress (RA) in the signal is a group address and whether the station isnot in the addressed group. If the receiving station address (RA) is agroup address and the station is not in the addressed group, controljumps to step 860, where the network allocation vector (NAV) is updated.If not, control continues to step 850.

In step 850, a determination is made as to whether the receiving stationaddress (RA) in the signal is a broadcast address and whether thestation is not a legacy station. If the receiving station address (RA)is a broadcast address and the station is not in the addressed group,control continues to step 860, where the network allocation vector (NAV)is updated. If not, control jumps to step 870. In step 870, the processends.

FIG. 9 is a flowchart illustrating a method of updating the networkallocation vector (NAV) in accordance with another exemplary embodimentof this invention. As shown in FIG. 9, the process begins with step 900,and continues to step 910, where the duration value is set. That is, inthis step, the duration value is set to a value other than a time periodfor subsequent transmission to spoof obeying stations. Control thencontinues to step 920.

In step 920, a signal, such as the request-to-send (RTS) signal is sentcontaining the set duration value. Next, in step 930, a determination ismade as to whether the receiving station address (RA) in the signal is abroadcast address. If the receiving station address (RA) is a broadcastaddress, control jumps to step 980, where the network allocation vector(NAV) is updated. If not, the receiving station address is not abroadcast address, control continues to step 940.

In step 940, a determination is made as to whether the receiving stationaddress (RA) in the signal is a multicast address. If the receivingstation address (RA) is not a multicast address, control jumps to step960. If the receiving station address (RA) is a multicast address,control continues to step 945.

In step 945, a determination is made as to whether the transmittingstation address (TA) is a unicast address and whether the station is notin the group identified by the multicast address. If the transmittingstation address (TA) is a unicast address and the station is not in thegroup, control jumps to step 980, where the network allocation vector(NAV) is updated. If not, control continues to step 950.

In step 950, a determination is made as to whether the transmittingstation address (TA) is a multicast address and whether the station isnot in the group identified by the multicast address contained in thetransmitting station address (TA). If the transmitting station address(TA) is a multicast address and the station is not in the groupidentified by the multicast address contained in the transmittingstation address (TA), control jumps to step 980, where the networkallocation vector (NAV) is updated. If not, control continues to step955.

In step 955, a determination is made as to whether the transmittingstation address (TA) is a broadcast address and whether the station isnot in the group identified by the multicast address. If thetransmitting station address (TA) is a broadcast address and the stationis not in the group, control jumps to step 980, where the networkallocation vector (NAV) is updated. If not, control jumps to step 990.

Next, in step 960, a determination is made as to whether the receivingstation address (RA) in the signal is a unicast address. If thereceiving station address (RA) is not a unicast address, control jumpsto step 990. If the receiving station address (RA) is a unicast address,control continues to step 965.

In step 965, a determination is made as to whether the transmittingstation address (TA) is the same unicast address as that contained inthe receiving station address (RA) and whether the station is not in thebasic service set (BSS) identified by the unicast address. If thetransmitting station address (TA) is the unicast address and the stationis not in the basic service set (BSS), control jumps to step 980, wherethe network allocation vector (NAV) is updated. If not, controlcontinues to step 970.

In step 970, a determination is made as to whether the transmittingstation address (TA) is a multicast address and whether the station isnot in the group identified by the multicast address contained in thetransmitting station address (TA). If the transmitting station address(TA) is the multicast address and the station is not in the group,control jumps to step 980, where the network allocation vector (NAV) isupdated. If not, control continues to step 975.

In step 975, a determination is made as to whether the transmittingstation address (TA) is a broadcast address and whether the station isnot in the basic service set (BSS) identified by the unicast address. Ifthe transmitting station address (TA) is a broadcast address and thestation is not in the basic service set (BSS), control continues to step980, where the network allocation vector (NAV) is updated. If not,control jumps to step 990. In step 990, the process ends.

FIG. 10 is a flowchart illustrating a method of resetting the networkallocation vector (NAV) in accordance with another exemplary embodimentof this invention. As shown in FIG. 10, the process begins with step1000, and continues to step 1010, where the CF-End message is sent. Inthis step, the CF-End indicates a value other than the end of thecontention free period to spoof obeying stations. Next, in step 1020, adetermination is made as to whether the receiving station address (RA)in the message is a broadcast address. If the receiving station address(RA) is a broadcast address, control jumps to step 1080, where thenetwork allocation vector (NAV) is reset. If not, the receiving stationaddress (RA) is not a broadcast address, control continues to step 1030.

In step 1030, a determination is made as to whether the receivingstation address (RA) in the signal is a multicast address. If thereceiving station address (RA) is not a multicast address, control jumpsto step 1050. If the receiving station address (RA) is a multicastaddress, control continues to step 1035.

In step 1035, a determination is made as to whether the transmittingstation address (TA) is a unicast address and whether the station is inthe group addressed by the receiving station address (RA). If thetransmitting station address (TA) is a unicast address and the stationis in the group, control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1040.

In step 1040, a determination is made as to whether the transmittingstation address (TA) is a multicast address and whether the station isin the group addressed by the receiving station address (RA). If thetransmitting station address (TA) is a multicast address and the stationis in the group addressed by the receiving station address (RA), controljumps to step 1080, where the network allocation vector (NAV) is reset.If not, control continues to step 1045.

In step 1045, a determination is made as to whether the transmittingstation address (TA) is a broadcast address and whether the station isnot in the group addressed by the receiving station address (RA). If thetransmitting station address (TA) is a broadcast address and the stationis not in the group addressed by the receiving station address (RA),control jumps to step 1080, where the network allocation vector (NAV) isreset. If not, control jumps to step 1090.

Next, in step 1050, a determination is made as to whether the receivingstation address (RA) in the signal is a unicast address. If thereceiving station address (RA) is not a unicast address, control jumpsto step 1090. If the receiving station address (RA) is a unicastaddress, control continues to step 1055.

In step 1055, a determination is made as to whether the transmittingstation address (TA) is a unicast address, whether the transmittingstation address (TA) matches the receiving station address (RA), andwhether the station is in the same basic service set (BSS). If thetransmitting station address (TA) is a unicast address, matches thereceiving station address (RA), and the station is in the same basicservice set (BSS), control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1060.

In step 1060, a determination is made as to whether the transmittingstation address (TA) is another unicast address and the station is atthe receiving station address (RA). If the transmitting station address(TA) is another unicast address and the station is at the receivingstation address (TA), control jumps to step 1080, where the networkallocation vector (NAV) is reset. If not, control continues to step1065.

In step 1065, a determination is made as to whether the transmittingstation address (TA) is a multicast address and whether the station isin the group addressed by the multicast address. If the transmittingstation address (TA) is a multicast address and the station is in thegroup, control jumps to step 1080, where the network allocation vector(NAV) is reset. If not, control continues to step 1070.

In step 1070, a determination is made as to whether the transmittingstation address (TA) is a broadcast address and whether the station isin the same basic service set (BSS) as the unicast address. If thetransmitting station address (TA) is a broadcast address and the stationis in the same basic service set (BSS) as the unicast address, controlcontinues to step 1080, where the network allocation vector (NAV) isreset. If not, control jumps to step 1090. In step 1090, the processends.

It should be appreciated that many other possibilities exist. That is,it should be appreciated that the exemplary embodiments discussed aboveare just a small list of examples of how the principles of the presentinvention can be applied. Other arrangements and methods an beimplemented by those skilled in the art without departing from thespirit and scope of the present invention.

1. A method for spoofing stations while transmitting data through amedium, the method comprising: sending a message to reset a networkallocation vector at a time other than an end of a contention freeperiod, wherein at least one of the stations is an obeying station thatresets a network allocation vector of the obeying station in accordancewith the sent message, wherein the sent message is a CF-End messagewherein the sent message indicates an end of a time period forsuppressing transmissions by the obeying station and transmissions ofunknown protocols are given preferential use of the medium when thetransmissions by the obeying station are suppressed.
 2. A method forspoofing stations while transmitting data through a medium, the methodcomprising: sending a message to reset a network allocation vector at atime other than an end of a contention free period, wherein at least oneof the stations is an obeying station that resets a network allocationvector of the obeying station in accordance with the sent message,wherein the sent message further comprises a transmitting stationaddress and a receiving station address wherein the sent messageindicates an end of a time period for suppressing transmissions by theobeying station and transmissions of unknown protocols are givenpreferential use of the medium when the transmissions by the obeyingstation are suppressed.
 3. The method of claim 2, wherein the networkallocation vector is reset if the transmitting station address is aunicast address, the receiving station address is a multicast address,and the obeying station is in a group identified by the multicastaddress.
 4. The method of claim 2, wherein the network allocation vectoris reset if the transmitting station address is a unicast address, thereceiving station address is the unicast address, and the obeyingstation is in a basic service set identified by the unicast address. 5.The method of claim 2, wherein the network allocation vector is reset ifthe transmitting station address is a first unicast address, thereceiving station address is a second unicast address, and a stationaddressed by the receiving station address is at the second unicastaddress.
 6. The method of claim 2, wherein the network allocation vectoris reset if the transmitting station address is a first multicastaddress, the receiving station address is a second multicast address,and the obeying station is in a group identified by the second multicastaddress.
 7. The method of claim 2, wherein the network allocation vectoris reset if the transmitting station address is a multicast address, thereceiving station address is a unicast address, and the obeying stationis in a group identified by the multicast address.
 8. The method ofclaim 2, wherein the network allocation vector is reset if thetransmitting station address is a broadcast address, the receivingstation address is a unicast address, and the obeying station is not ina basic service set identified by the unicast address.
 9. The method ofclaim 2, wherein the network allocation vector is reset if thetransmitting station address is a broadcast address, the receivingstation address is a multicast address, and the obeying station is notin a group identified by the multicast address.
 10. The method of claim1, wherein the sent message indicates an end of a time period forsuppressing transmissions by the obeying station and transmissions ofhidden stations are given preferential use of the medium when thetransmissions by the obeying station are suppressed.
 11. The method ofclaim 1, wherein the sent message indicates an end of a time period forsuppressing transmissions by the obeying station and criticaltransmissions are given preferential use of the medium when thetransmissions by the obeying station are suppressed.
 12. The method ofclaim 1, wherein the sent message indicates an end of a time period forsuppressing transmissions by the obeying station and at least some ofthe stations are provided in an overlapping basic service set, andstations of the overlapping basic service set are given preferential useof the medium when the transmissions by the obeying station aresuppressed.
 13. The method of claim 1, wherein the sent messageindicates an end of a time period for suppressing transmissions by theobeying station and stations of an enhanced version of a standard aregiven preferential use of the medium when the transmissions by theobeying station are suppressed.
 14. A machine-readable medium havingstored thereon a plurality of executable instructions, the plurality ofexecutable instructions comprising instructions to: send a message toreset a network allocation vector at a time other than an end of acontention free period, wherein at least one of a plurality of stationsis an obeying station that resets a network allocation vector of theobeying station in accordance with the sent message, wherein the sentmessage further comprises a transmitting station address and a receivingstation address wherein the sent message indicates an end of a timeperiod for suppressing transmissions by the obeying station andtransmissions of unknown protocols are given preferential use of themedium when the transmissions by the obeying station are suppressed. 15.The machine-readable medium of claim 14, wherein the sent message is aCF-End message.
 16. The machine-readable medium of claim 14, wherein thenetwork allocation vector is reset if the transmitting station addressis a unicast address, the receiving station address is a multicastaddress, and the obeying station is in a group identified by themulticast address.
 17. The machine-readable medium of claim 14, whereinthe network allocation vector is reset if the transmitting stationaddress is a unicast address, the receiving station address is theunicast address, and the obeying station is in a basic service setidentified by the unicast address.
 18. The machine-readable medium ofclaim 14, wherein the network allocation vector is reset if thetransmitting station address is a first unicast address, the receivingstation address is a second unicast address, and a station addressed bythe receiving station address is at the second unicast address.
 19. Themachine-readable medium of claim 14, wherein the network allocationvector is reset if the transmitting station address is a first multicastaddress, the receiving station address is a second multicast address,and the obeying station is in a group identified by the second multicastaddress.
 20. The machine-readable medium of claim 14, wherein thenetwork allocation vector is reset if the transmitting station addressis a multicast address, the receiving station address is a unicastaddress, and the obeying station is in a group identified by themulticast address.
 21. The machine-readable medium of claim 14, whereinthe network allocation vector is reset if the transmitting stationaddress is a broadcast address, the receiving station address is aunicast address, and the obeying station is not in a basic service setidentified by the unicast address.
 22. The machine-readable medium ofclaim 14, wherein the network allocation vector is reset if thetransmitting station address is a broadcast address, the receivingstation address is a multicast address, and the obeying station is notin a group identified by the multicast address.